1. Field of the Invention
The present invention relates to a method and an apparatus for generating an image file storing a group of image data sets representing a group of still images photographed in such a manner that 2-dimensional coordinates, a viewpoint, and the like thereof are different for each image, and to a method and an apparatus for progressively reproducing the image file, as well as to a computer-readable recording medium storing a program to cause a computer to execute these methods.
2. Description of the Related Art
As a method for realistically representing an image of a scene or of an object, a method of interactive reproduction of a group of still images comprising images whose spatial relationships to each other have been predetermined is known. For example, for a group of still images obtained by photographing an object from multiple directions at an equal angle interval, an image with a changing viewpoint can be reproduced interactively by reproducing a still image first and by specifying a direction of rotation of the object with a mouse or the like. For a group of still images obtained by photographing with a focal point changing gradually from the near distance to the far distance, objects in the near and far distances can be displayed clearly by interactively changing the focal point. As has been described above, a group of still images can be reproduced interactively when the group of still images are obtained by changing display dimensions in various ways, such as changing a viewpoint at the time of photographing up and down, right and left, and back and forth, or changing a focal point, or changing an interval of photographing a moving object.
Meanwhile, as a format for storing image data, various formats such as JPEG, GIF, and TIFF have been known. According to another format proposed recently, image data are decomposed into a hierarchy based on resolution or density resolution and data at each layer of the hierarchy (hierarchical data) are stored after coding and compression thereof. More specifically, according to this storage format, image data are decomposed into hierarchical data according to multiple resolutions or density resolutions through wavelet transform or the like carried out thereon, and the hierarchical data at each resolution or density resolution are coded and compressed according to the hierarchy and saved in a file.
This storage format has the following characteristics:
(1) Unlike a DCT (Discrete Cosine Transform) method used in the conventional JPEG format, no artifacts such as block distortion are created, since image data are not processed in blocks.
(2) Only resolution information which is necessary upon transfer of image data needs to be transferred, since the image data have been coded hierarchically. This enables efficient image transfer.
(3) Various kinds of image processing such as frequency enhancing processing can be carried out comparatively easily, since image data are decomposed into data at multiple resolutions or multiple density resolutions.
(4) Simultaneous decomposition of space and frequency according to multiple-resolution analysis is possible. In a low frequency range wherein coding efficiency is greatly affected, an orthogonal transform is carried out in a wide range, whereas in a high frequency range, an orthogonal transform is possible in a narrow range. Therefore, even when quantization noise near an edge of an image is generated, spatial spread of the noise can be suppressed. As a result, the noise is not easy to perceive.
Like a FlashPix file proposed by Eastman Kodak Co., a file format enabling storage of data sets having different characteristics in a file has also been proposed. Hierarchical data decomposed into multiple resolutions or density resolutions can be stored in such a file according to the FlashPix standard.
When image data comprising hierarchical images, such as in the above-described format file or a FlashPix standard file, are displayed on a monitor or the like, data transfer to the monitor and image reproduction on the monitor is carried out from a low resolution or low density resolution (hereinafter, simply expressed as resolution) to high resolution. This is called progressive transfer (or progressive reproduction in the case of reproduction). When the data transferred progressively are displayed on a monitor, an entire low resolution image is displayed first, and images with gradually improving clarity are reproduced in accordance with increasing resolution of the data.
By interactively reproducing a group of still images as has been described above, reproduced images can be provided with reality and liveliness. However, image data representing such a group of still images have a substantially large amount of information and transfer thereof is not efficient. For example, when a group of still images are generated by photographing an object from viewpoints all around the object, in order to reproduce the images smoothly, angular resolutions of at least 60 divisions and 15 divisions in horizontal and vertical directions respectively are necessary. Therefore, at least 900 angular display dimensions are necessary, and the amount of the image data thus becomes 900 times that of a still image. Therefore, when all images in the group of still images are transferred and reproduced, interactive display of the images is time-consuming. Furthermore, by transferring and reproducing the still images frame by frame, the content of the image can be understood to some degree, but the group of still images cannot obtain the interactive characteristic which the image group should have, until all the images are transferred.
The present invention has been created based on consideration of the above problems. An object of the present invention is to provide a method and an apparatus for generating an image file to enable reduction in reproduction wait time when a group of still images such as the one described above are interactively reproduced, and a method and an apparatus for progressively reproducing the image file, as well as a computer-readable recording medium storing a program to cause a computer to execute the methods.
An image file generating method of the present invention is a method of generating an image file storing a group of image data sets representing a group of still images comprising a plurality of still images having predetermined spatial relationships to each other, and the method comprises the steps of:
obtaining hierarchical image data in each hierarchical layer by forming the group of image data sets into a hierarchy in such a manner that the number of display dimension divisions in one hierarchical layer is larger than that of a preceding layer; and
storing the hierarchical data in each hierarchical layer in the image file.
xe2x80x9cHaving predetermined spatial relationships to each otherxe2x80x9d means that changes in a viewpoint, a focal point, a position on the move, a resolution, and the like of an object included in the group of still images are interactively reproducible, as in the case where the object is viewed from different positions, or have different focal points, photographing intervals, or resolutions.
The xe2x80x9cdisplay dimensionxe2x80x9d means a dimension used upon interactive reproduction of the group of still images, and the viewpoint position, the focal point position, the photographing interval, the resolution and the like can be listed as the dimension. Not only 1 display dimension but also a plurality of display dimensions can be used.
The phrase that xe2x80x9cthe number of display dimension divisions in one hierarchical layer is largerxe2x80x9d means that at least one of the numbers of the viewpoints, the focal points, the photographing intervals, the resolutions, and the like is larger than the number of display dimension divisions of the preceding hierarchical layer. In this specification, xe2x80x9chaving a higher display dimensionxe2x80x9d means that the number of display dimension divisions is large.
Out of the image data in each hierarchical layer, it is preferable for hierarchical image data having a smallest number of display dimension divisions to be composed of image data of an image or an image group representing the group of still images.
It is also preferable for the image data in each hierarchical layer to be obtained by relating corresponding images in each hierarchical layer.
When a still image in one hierarchical layer is considered, a plurality of still images corresponding to the still image exist in a subsequent display dimension. Therefore, xe2x80x9crelating the corresponding images in each hierarchical layerxe2x80x9d means to relate the still image at the hierarchical layer with the plurality of still images corresponding to the still image in the subsequent display dimension.
It is also preferable that a plurality of the display dimensions are set.
The phrase that xe2x80x9ca plurality of the display dimensions are setxe2x80x9d means that the group of still images are set to have any different display dimensions out of the viewpoints, the focal points, the photographing intervals, the resolutions, and the like describe above, for example.
An image reproducing method of the present invention is a method of progressively reproducing an image file generated according to the image file generating method of the present invention, and the image data are reproduced from hierarchical image data having a smallest number of display dimension divisions out of the hierarchical image data in each hierarchical layer.
In the case where corresponding images at each hierarchical layer are related to each other, it is preferable for the image data to be reproduced from those having the smallest number of display dimension divisions out of the hierarchical data, and at the time hierarchical image data having a predetermined display dimension are reproduced, hierarchical image data to be reproduced after the predetermined dimension and related to an image specified in the predetermined dimension are preferably reproduced in priority to the other image data.
It is preferable for the hierarchical image data to be reproduced based on a pre-set display dimension, in the case where the plurality of display dimensions are set.
An image file generating apparatus of the present invention is an apparatus for generating an image file storing a group of image data sets representing a group of still images comprising a plurality of still images having predetermined spatial relationships to each other, and the image file generating apparatus comprises:
hierarchy forming means for obtaining hierarchical image data in each hierarchical layer by forming the group of image data sets into a hierarchy in such a manner that the number of display dimension divisions in one hierarchical layer is larger than that of a preceding layer; and
recording means for storing the hierarchical data at each hierarchical layer in the image file.
It is preferable for the hierarchy forming means to obtain the image data in each hierarchical layer in such a manner that image data in a hierarchical layer having a smallest number of display dimension divisions are composed of image data of an image or an image group representing the group of still images.
It is also preferable for the hierarchy forming means to obtain the image data in each hierarchical layer by relating corresponding images in each hierarchical layer.
It is also preferable for the hierarchy forming means to obtain the image data in each hierarchical layer by setting a plurality of the display dimensions.
An image reproducing apparatus of the present invention comprises reproduction means for progressively reproducing an image file generated by the image file generating apparatus of the present invention and the reproduction means reproduces image data in an order starting from hierarchical image data having a smallest number of display dimension divisions out of the hierarchical image data.
In the case where the image file generating apparatus generates the hierarchical image data by relating corresponding images in each hierarchical layer, it is preferable for the reproduction means to reproduce the image data from the hierarchical image data having the smallest number of display dimension divisions out of the hierarchical data, and at the time hierarchical image data having a predetermined display dimension are reproduced, hierarchical image data to be reproduced after the predetermined dimension and related to an image specified out of the images in the predetermined dimension are preferably reproduced in priority to the other image data by the reproduction means.
It is preferable for the reproduction means to reproduce the hierarchical image data in each hierarchical layer based on a pre-set display dimension, in the case where the image file generating apparatus generates the hierarchical image data by setting a plurality of display dimensions.
The processing carried out in the image file generating method and in the image file reproducing method may be provided as a program recorded in a computer-readable recording medium to cause a computer to execute the processing.
According to the present invention, an image file is generated by forming a hierarchy of the image data sets representing a group of still images so that the image data sets have different display dimension divisions. When the display dimension of image data in a hierarchical layer is low, the amount of image data in the layer is comparatively small. Therefore, in the case where the image file is progressively reproduced from the hierarchical image data having the low display dimension, the display dimension is low at an early stage of reproduction, but enables earlier confirmation of the content of an image represented by the image file than in the case where the entire image data sets are transferred. Furthermore, although the number of display dimension divisions is small at an early stage, images can be reproduced having some degree of interactive characteristic, since the early stage hierarchical data includes a plurality of still images having different display dimensions.
Moreover, by forming the hierarchical image data having the smallest number of display dimension divisions from image data representing the group of still images, the time necessary for confirmation of the content of an entire reproduced image can be further shortened, since the content of the image file can be confirmed immediately at the time the hierarchical image data are reproduced.
When the corresponding image data in each hierarchical layer are related to each other, by specifying an image out of still images in a predetermined dimension reproduced at one stage, images related to the specified image can be reproduced in priority to the other images having dimensions larger than that of the specified image. In this manner, a desired image can be reproduced earlier than the others, and users"" needs can be met.